This is an example of letting your stutter control you, my advice is to try to not worry about it and say what you feel. Listen, you love your fiancee, right? You have all these words inside of you that you want to use to let her/him know that, right? Then say the words, and say them with pride. If it takes you a little bit longer than the average person to express yourself, then so be it. Your friends, if they're really your friends, won't care. Your family shouldn't care. God knows your fiancee doesn't care. I get that it's hard to get past the embarrassment or shame, but this is one of the most important days of your life. Own it, this is your day. The worst thing that could possibly happen is the people listening have to listen for a little bit longer than usual. Trust me, they'll get over it, and you'll be happier for saying exactly what it is you want your fiancee to hear. Congrats, and good luck.